Gene therapy refers to the correction of genetic defects by injecting a new gene constructed by using a DNA recombinant method into cells of a patient, or to the prevention or treatment of genetic defects such as cancer by genetic modification of cells, infectious diseases or autoimmune diseases by adding new functions to the cells. However, because polynucleotides including genes may be easily cleaved by degrading enzymes present in cells and cellular membranes and polynucleotides are all strongly negatively charged, it is very difficult for polynucleotides to pass through cellular membranes to be delivered to cells. The efficiency of polynucleotides to be introduced into cells is very low and thus much research on gene delivery systems for delivering polynucleotides has been actively conducted in order to address these problems.
As a delivery system for delivering polynucleotides into target cells, viral and non-viral delivery systems may be used. Although viral delivery systems have high transfection efficiency, there are limitations in applying the systems to humans due to disadvantages in that their manufacturing processes are complex and the systems have safety issues such as immunogenicity, infection potential, inflammation production, insertion of non-specific polynucleotides, etc. and there are limitations in terms of the sizes of polynucleotides that can be accommodated.
Accordingly, non-viral delivery systems have been recently highlighted as a replacement for viral delivery systems. Non-viral delivery systems are advantageous in that a minimal immune response may lead to repeated administration, a specific delivery to a specific cell may be allowed, and mass production may be easily achieved. Among non-viral delivery systems, cationic polymers which allow a polynucleotide-polymer complex to be formed through ionic bonding to polynucleotides which are negatively charged have been recently highlighted. For example, the cationic polymers include poly-L-lysine, polyethyleneimine, poly[α-(4-aminobutyl)-L-glycolic acid], etc., and these pressurize polynucleotides to form nanoparticles and protect polynucleotides from enzymatic cleavage, and are rapidly penetrated into cells to aid in exiting from endosomes. In particular, it is well known that polyethylene imine effectively pressurizes plasmid DNA to be made into colloidal particles and has high polynucleotide delivery efficiency due to a buffering capability of pH reactivity to effectively deliver polynucleotides in vitro and in vivo to a variety of cells.
However, as conventional cationic polymers have increased molecular weights, interaction with polynucleotides increases and thus the polymers are stably introduced into cells. An extremely strong interaction prevents polynucleotides from being efficiently released and polynucleotides are introduced in the form of a complex into a nucleus, which causes toxicity or lowers polynucleotide delivery efficiency. In addition, these cationic polymers interact with plasma proteins present in blood or are removed by reticuloen-dothelial system, the stability of the cationic polymers in blood is so low that it is difficult to use in practically clinical applications.
In particular, a blood brain barrier (BBB) is a membrane which protects the central nerve system and has a compact structure that prevents external materials from being easily introduced, and thus it is difficult to deliver drugs and genes due to limited permeability.
Thus, there is a need for a reducible polynucleotide delivery system which provides long-lasting circulation and safety in blood, exhibits efficient polynucleotide delivery efficiency, and has low toxicity. In addition, there is a need for a polynucleotide delivery system which may introduce polynucleotides into brain cells in order to treat neurodegenerative diseases.